The present invention relates to a method and a device for controlling an internal combustion engine.
Such a method and such a device for controlling an internal combustion engine are known, for example, from the German Published Patent Application No. 195 27 218. There, a method and a device are described for regulating the smooth running of an internal combustion engine, in which a control deviation and a governor are allocated to each cylinder of the internal combustion engine. Each governor stipulates a cylinder-specific triggering signal on the basis of the allocated control deviation.
The aim of this procedure is to equalize the fuel quantity metered to the individual cylinders. Differences in the metered fuel quantity between the individual cylinders are equalized. In this context, it may occur that although the same fuel quantity is metered to all the cylinders and/or all the cylinders contribute the same torque to the total torque, the individual cylinders receive different air quantities metered in. The result is that increased exhaust-gas emissions, particularly particle emissions, occur at individual cylinders. When working with the related art, these increased emissions can only be decreased by reducing the total injection quantity and/or the average value of the cylinder-individual fuel quantities to the extent that the emissions are minimized. This quantity reduction leads to a decrease in the performance of the internal combustion engine.
Because cylinder-specific actual values are determined on the basis of a signal from a sensor arranged in the exhaust train and are compared to a setpoint value, and because triggering signals for the cylinder-individual control of the fuel quantity and/or air quantity are specifiable on the basis of the comparison, the exhaust-gas emissions can be markedly reduced, the power output of the internal combustion engine not being impaired.
Preferably, sensors are used which provide a signal that characterizes the oxygen concentration in the exhaust gas, or a signal which characterizes the pressure in the exhaust gas.
The lambda values, i.e. the oxygen concentrations, of all cylinders are preferably equalized. In this context, both the injected fuel quantity and the supplied air quantity, which is adjustable, for example, with the aid of a cylinder-individual exhaust-gas recirculation, are used as a manipulated variable. In the following, the procedure is described using the fuel quantity as an example.
It is particularly advantageous if the procedure is combined with a smooth-running control according to the related art.
According to the present invention, it was recognized that a particularly simple signal conditioning lies in the fact that the signal of the sensor arranged in the exhaust train is able to be filtered using at least two filtering elements having different frequencies; at least two frequency-specific actual values, a setpoint value and frequency-specific control deviations are determinable on the basis of the filtered signal.
A particularly meaningful signal is yielded if, to make the frequency-specific quantities available, the output signal of the sensor arranged in the exhaust train is able to be filtered by at least two band-pass filters with adjustable mid-frequencies, the mid-frequencies lying at integral multiples of the camshaft frequency.
Furthermore, of particular importance are the implementations in the form of a computer program having a program-code element, and in the form of a computer program product having the program-code element. The computer program of the present invention has the program-code element for carrying out all the steps of the method according to the present invention when the program is executed on a computer, particularly a control unit for an internal combustion engine of a motor vehicle. Thus, in this case the present invention is implemented by a program stored in the control unit, so that this control unit provided with the program represents the present invention in the same way as the method for whose accomplishment the program is suitable. The computer program product of the present invention has the program-code element which is stored on a machine-readable data carrier in order to carry out the method of the present invention when the program product is executed on a computer, particularly a control unit for an internal combustion engine of a motor vehicle. Thus, in this case the present invention is implemented by a data carrier, so that the method of the present invention can be carried out when the program product, i.e. the data carrier is integrated into a control unit for an internal combustion engine, particularly of a motor vehicle. In particular, an electrical storage medium, e.g. a read-only-memory (ROM), an EPROM or even an electrical permanent storage such as a CD-ROM or DVD may be used as data carrier or as computer program product.